A population-based study of lung cancer risk among relatives of lung cancer cases and controls is proposed. Families of lung cancer patients will be identified through two case series: 1) non-smoking lung cancer patients aged 40-84 who participated in a previous study of lung cancer risk factors and 2) newly diagnosed lung cancer patients under the age of 40. These two groups are likely to demonstrate a genetic component to risk. All lung cancer cases will be ascertained through the Metropolitan Detroit Cancer Surveillance system of the Division of Epidemiology of the Michigan Cancer Foundation, a participant in NCI'S SEER program. Control families will be identified through random digit dialing. Telephone interviews will be conducted with the lung cancer case or control and several family members for each family included in the study. In addition to risk of lung cancer among relatives, risk of other cancers and other respiratory diseases also will be investigated. Risks associated with cigarette smoking and occupational exposures will be included in the analysis. Various measures of familial risk will be used in the determination of disease risk among relatives after adjustment for individual risk factors (smoking history, age, sex, race, birth cohort, and occupation). It will be possible to investigate familial risks in terms of age at diagnosis and histologic type of the lung cancer diagnosed in the proband. The modification of a new statistical method appropriate for the analysis of family data is proposed in conjunction with more conventional approaches to the analysis. High and low risk families can be identified for entry into future studies of molecular and genetic markers for disease.